If there is no ACTUAL center diff'l then the VC use must be as stated in #1.

That places the VC in "series" with the rear driveline, just as in the Chrysler T&C, and there is evry little torque to the rear unless the VC has reason to "tighten up". The more recent problem with this type of VC F/awd implementation is that TC activation, INSTANT TC activation, upon even the slightest level of front wheelspin/slip, prevents the VC from EVER tightening.

That's the main reason Chrysler discontinued the F/awd T&C, the adoption of TC (and "VSC") made their VC implementation non-functional, useless.

Even a beginning automotive design engineer could put the fallacy to that statement. Even the new Subbies with the ECU controlled clutch pak only route engine torque to the rear for times, during acceleration, when excessive drive torque is most likely to result in front wheelspin/slip

If that were to be so your tire treads would have an a very short life and early, premature driveline component failures would be the NORM.

"..When the axles spin at different rates..." TC will INSTANTLY activate, fully dethrottling the engine while simultaneously braking the driven, front, wheels to alleviate the potential for loss of directional control.

With the advent, adoption, of TC it is not possible for a VC to be functional absent a TC off capability. Additionally, actual VC functionality, assuming TC off, will always compromise ABS and stability controls.

As a result of the above limitations/restrictions most modern day systems using a VC have had the fluid reformulated such that the VC remains forever flaccid.

PRE-EMPTIVELY sends more power to the rear axle, "needed" or no, at times when loss of directional control is most likely to otherwise result. Those times fall into only 2 categories, low speed acceleration, and when turning tightly or turning while accelerating.

Other than those times the system will default into a definite front torque biasing mode. Regardless of the instantaneous mode of operation loss of directional control is such a dire threat for FWD or F/awd vehicles that the INSTANT response to wheelspin/slip, DRIVEN (front) wheelspin/slip, will be activation of TC.

I got stuck recently in the Sierras when I backed over a large angular piece of granite that dropped the right rear wheel into a hole. All the other wheels were firmly on the ground and the chassis did not high center. I thought the AWD in the 5-speed would pull me out with no problem. But all it did was spin the right rear wheel and burn up the clutch. I managed to get out by slipping the jack under the chassis in front of the right rear wheel and jacking up the car enough to put some rocks and large branches under the wheel and the floor matte over the rocks/branches and up the rock, and I finally got out. But I was very disappointed in the car. So, what gives? Thanks. LRV

Subaru is not shy regarding marketing "AWD" systems that have VERY serious shortcomings. The current WRX, for instance, uses a completely non-functioning VC, Viscous Clutch, in order to tout "AWD" capability.

Sounds as if your's is one of the many F/awd systems out there in the market today that are really "ONE-WHEEL" drive systems. Totally open center differential, "AWD" mode only if all four tires have roughly EQUAL traction.

Most of those have a TC implemented "AWD" system, braking of "slipping" wheels to simulate traction accompanied INSTANTLY by full engine dethrottling...not very helpful in the situation you describe.

Since turning off TC results in the car reverting to a simple ONE-WHEEL drive he got exactly the results one would expect.

With TC on the engine dethrottling would have been so severe the engine torque wasn't enough to pull that wheel over the "hump".

TC off functionality is pretty much restricted to "feathering" the throttling right up to, but not beyond, the point of loss of traction. Wheelspin, rocking the car back and forth, to get unstuck, can also be used constructively.

VDC wasn't available on the 2.5L models until 2008 as an option, then standard in 2009.

Even so, the car should have had traction in the front axle unless the center differential had gone out. It's unusual that he would have power to the rear axle under that circumstance, though, as typically it is the rear axle that would stop working as opposed to the front axle. In 2007, 08, and 09, the rear axles on the Outback were limited slip, but they were open prior to (and after) that, so under limited traction conditions they are generally 2wd (one on each axle).

I managed to get my '96 Outback stuck more than a few times in deep snow by taking too much weight off the wheels, and it would always default to spinning the left front and right rear tires. :blush:

That would be strange indeed. Even as far back as 2001 it ws well understood industry wide that TC could prevent a LOT of loss of control accidents rising from the use of to much engine torque applied to the drive wheels.

Prior to that period TC was found mostly only on "pure" FWD vehicles, non-AWD versions.

That was one of the aspects facilitated by DBW, the engine could be dethrottled without compromising the catalytic converter.

VDC probably refers to stability control INCLUSIVE of TC, the 2008 timing would be about right for that happenstance.

Not knowing anything at all about the specifics of this particular "AWD" system in question the description, only the wheel with traction spinning freely, indicates a fully open center diff'l with the TC turned off.

"..were limited slip..."

But more likely than otherwise "simulated" limited slip using TC braking.

Sounds as if your '96 had some method to automatically "lock" the center diff'l or PTO, VC's were commonly used for that back then. Once TC was implemented those methods because useless, non-functional.

I know of a few high end marques that use VC(s) to implement a form of rear diff'l LSD but I suspect in Subbies case you mean center diff'l or PTO drive "locking" is done using a VC.

"..The WRX retains a rear LSD,..."

That, an actual mechanical LSD, would be a bit of foolishness since the current WRX model has no means for driving the rear diff'l except under TC braking, along with full engine dethrottling, of the front wheels. Probably not even then unless you use an extended period of TC activation.

The above assumes the WRX's VC center "locking" is at least minimaly functional, not something I have any faith in at all.

"..STi...has both..."

I'm willing to bet you good money that if the Sti has a rear LSD it is of a "virtual" nature using "differential" rear wheel braking.

And front LSD...??!!

NOT.

Those are found ONLY on the most robust off-road vehicles (Hummer, etc.)wherein the driver is expected to be fully aware, expectent, experienced, with what a front LSD will do to your fingers, thumbs, etc.

I think you will find that the Subbies version of front LSD is via TC braking and of BOTH wheels simultaneously even if only one wheel is slipping. To do otherwise would often result in yanking the stearing wheel right out of the hands of an unwary driver not expecting the resulting hard "TUG".